Large mirage effect in supercritical CO2

A laser beam is bent when it passes through a region that has a gradient of refractive index lying perpendicular to its path. This effect is responsible for common ‘mirages’. We created a refractive index gradient in supercritical CO2 by means of a vertical temperature gradient. For this highly compressible fluid, a small temperature gradient implies a large density gradient, which in turn, leads to a large refractive index gradient. Thus the bending is much larger than that from normal liquids. We used a He–Ne laser to demonstrate this large effect in pure supercritical CO2 and modeled it with the use of well-established physical parameters.